The rapid development of computer and information technology has resulted in great demand for high capacity storage devices. Currently, these storage devices are being pushed to their limits by applications as diverse as digital video editing and genomics. Therefore, the data storage industry is continually under pressure to increase the capacity of data storage devices. One of the primary methods to increase capacity is to increase the recording density of the magnetic recording media in most storage devices. To achieve an ultra-high recording density of, for example, about 100 Gbits/inch2 or higher, magnetic recording media are required to possess a low remnant-thickness product (Mrδ), a high coercivity (Hc) as well as a high signal-to-media noise (S/Nm).
In a conventional magnetic recording media, such as a Cobalt (Co) based alloy, non-magnetic elements such as Chromium (Cr) and/or Boron (B) are incorporated into the thin film magnetic recording media to reduce the grain size as well as to reduce the intergranular coupling effect of the magnetic particles in the recording media. The result is a magnetic recording medium having a grain size of about 8–12 nanometers (nm) with a distribution width of about 20% or more. In this context, the term “distribution width” denotes the Full Width at Half Maximum (FWHM) height of the grain size distribution.
In order to obtain a high S/Nm magnetic recording media, the grain size and their distribution width as well as the intergranular coupling between the magnetic gains must be properly controlled to further scale down.
Reduction of grain size for Co-based alloy recording media is limited by the thermal-instability of the magnetic grains or particles, commonly referred to as the “superparamagnetism” effect. Attempts to overcome this limitation are illustrated in “Effect Of Magnetic Anisotropy Distribution In Longitudinal Thin Film Media” by Hee et al (J. Appl. Phys., Volume 87, 5535–5537, 2000) and U.S. Pat. No. 6,183,606 to Kuo et al. The Hee article discloses a method using highly oriented media to allow further reduction of the grain size. In contrast, the Kuo patent uses L10 ordered FePt or CoPt material to form longitudinal or perpendicular magnetic recording media with very small magnetically stable grains.
While the above methods provide possibilities to obtain magnetically stabled grains with further reduced size in a first place, in the subsequent post-deposition annealing process, a high temperature, for example 600° C. or above, is to apply to the substrate in order to obtain recording media with an appropriate crystallized structure or with chemically ordered L10 FePt or CoPt. Unfortunately, this high temperature annealing process also increases gain size from about 10 nanometers nm) to about 3 nm in the deposited thin film, which eventually reduces the recording density. In addition, no solution is provided by these methods to control the grain distribution width. Due to the larger grain size and their wide distribution width, these films have presented rather poor recording properties, in particular a very low S/Nm. Moreover, the high-temperature annealing process is not compatible with existing magnetic recording media fabrication process and materials.